Not really. There are public restrooms on the pool deck, but they are small and crammed that first afternoon with people changing. I suggest wearing your bathing suits under your clothes that morning rather than trying to get changed in a bathroom.

Another vote for swimsuits under clothes. The restrooms in the terminal are better for changing than on the ship (if you are flying in, you may not want swimsuit under clothes from early morning). There are "family" restrooms that bigger, but these are relatively few.